If you live in the US or several other places, you probably know that the "good" Sudafed is kept behind the counter, and you have to sign for it. You may have also noticed that there is another version, called "Sudafed PE", that you can just pick up off the shelf.
A lot of people have done that and concluded for themselves that the PE version didn't work. That's why there are so many people commenting that they already knew the thing the article is about.
So... a lot of people were familiar with "PE", and apparently a lot of them knew that it stood for "phenylephrine". And it all touches on a bunch of existing controversy about why the effective medication is locked up.
It wasn't always. People knew that Sudafed was an pretty effective drug. (It was even used, under a different brand, on Apollo missions -- there was a TV ad with an astronaut endorsing it.) A lot of people are grumpy that a well-known effective medicine was made hard to get, and something else sneakily substituted.
The point being, it's not entirely a surprise that people are aware of the phenylephrine -- especially if they're older than, say, 40, and live in the United States. They remember, sniffily, when cold medicine started to suck.